(For those who haven't read my introduction I'm mtf pre-everything. Started going to a therapist though).  I know it must be rather common, but I find it very difficult to concentrate and feel like I may start crying just about anytime. At home it's no problem but at the university or somewhere out it's rather terrifying.
Any tips on how to control it? (kinda)

For me, deep breathing helps a lot - focusing on the breath going in and out, the feeling of my body, the way my ribs move, etc.  It takes me out of my head and really helps me get past it.  Also, I find myself more likely to cry spontaneously the longer I've held it in.  When that pressure builds up and I get a chance to let go in private, I try not to control myself, instead I feed in all those emotions and let the tears roll.  Eventually I just run out of cry.  A couple times letting the pressure out like that and the feeling of crying over anything seems to let up.

It is really difficult for me, too. I can cry so easily these days. Sometimes just thinking how my life is going is enough to cry. When I get dry eyes and they get irritated, no problem, I can clear that up in a hurry just by thinking of something in my life. The tears really roll!

I know from experience how hard it can be to hold back the tears. I learned to control it over the years so well that from 5th grade in primary school nobody saw me crying until a few years ago when I started to open up to some other trans* people.

Concentrating on the task you are doing, taking a deep breath in through your nose and exhale through your mouth can help in calming down a little and avoid crying.
Ultimately I don't think it is healthy to hold back tears but I can understand your reasons. I'm the same way nowadays at my new job where I have to prove my worth while I'm struggling with my problems and cannot risk coming out yet.
Sometimes I don't even realize how bad it is while I'm working and at the end of the day I just break down crying.

I would worry more about the Why. Crying all the time sounds like you are chronically to profoundly depressed. Better living through modern chemistry may help.

During the now occasional dark times I now have the trick I "try" to use is distraction. People have a bad habit of dwelling on the painful stuff. Thinking about what is making you down is a sure fire way to get more depressed and start to cry. I know I more often then not wallow in self pity though I know better.